Treatment of rubber



. a nitroso group Patented Oct. 14, 1941' UNITED STATES PATENT OFFICE TREATMENT OF RUBBER Philip T. Paul, Naugatuck, Comm, assignor, by 1 mesne assignments, to United States Rubber Company, New York, N.

New Jersey 12, a corporation oi No Drawing- I Application July 7, 1937, Serial No. 152,373

7 Claims.' (GI. 260-808) This invention relates to the treatment of rubber and similar oxidizable' materials, and more particularly to a new class of deterioration retarders.

An object of the invention is to provide a new class of anti-oxidants or age resistors for organic substances which tend to deteriorate by absorption of oxygen from the air, for example goods of rubber or allied gums, unsaturated fatty oils such as unsaturated vegetable oils, essential oils, petroleum oils and their derivatives such as gasollnes, soaps aldehydes, synthetic resins, and the like. A further object of the invention is to provide chemicals which additionally act as flexlmprovers or anti-flex cracking agents for vuletc. radicals. A may also be a divalent heterocyclic group of which N is a part, for example penta methylene or oxydiethylene.

The invention, however, is more particularly concerned with esters of hydroxy substituted aromatic secondary amines and boric acid, more particularly those esters of aryl aminophenolaxwhich are devoid of adjacent hydroxyl'groups in the phenolic nucleus.

A reaction occurs between ,boric acid I and a hydroxy aryl compound not containing a canized rubber such as tire treads, which under go repeated strains during use. Further objects will be apparent from the following description.

Broadly the invention comprises incorporating in the organic substance a compound of the type formula (it-OM-X where X represents a radical or group free of members of the carbon-sills con group of the peflodic system which radical or group is capable of forming with oxygen an,

anhydride of an inorganic acid. As illustrative of particular preferred embodiments, employing proximately equimolecular proportions of p- 4 hydroxyl group on an adjacent carbon atom. A,

typical illustration is the reaction between boric acid and p-hydroxy diphenylamine with the elim-, ination of water. .An intimate mixture of aphydroxy diphenylamine and boric acid are stirred and heated on a metal bath. The bath temper- .ature is raised to 220 C. and kept at that point until no more water is evolved. Final traces of waterare eliminated by raising the bath temperature to 300 C. and lowering the pressure to such a radical or group; the type formula may be expressed l A.N.RO

' X represents a residue from an inorganic acid such -asfrom'.boric, sulphuric or phosphoric acid; 0 represents oxygen; R is an aryl nucleus having no substituenthydroxyl groups adjacent to O; n is a whole number; A represents hydrogen; aryl or alkyl.

N is singly bonded to A andthe aryl group R, and it is additionally connected to Y which may or NHz as in the group be hydrogen R may be additionally-connected a nuclear carbon atom toany of the following radicals, amino, nitro, halogen, alkoxy, (saturated or unsaturated) aryloxy, aralkoxy, secondary or tertiary alkyl amino, secondary or tertiary aryl amino, alkyl, mercapto; etc. A, ,where it is alkyl or aryl,

- may be additionally connected to other radicals,

for example, in the case of aryl it may or may not be substituted by one or more hydroxyl, primary, secondary or tertiary amino, nitro, alkoxy, alkyl, aryloxy, hydroxy, alkyl, unsaturated alkyl,

3- mm. of mercury. The product is awesinous solid.

The boric acid or an equivalent of boric oxide may be reacted in the proportion of one, two or three mols to one or .two of the aryl hydroxyl compound following the above procedure to yield the. corresponding esters.

The mechanism of the reaction is not definitely understood. The mechanism might involve first elimination of water from boric acid to form various meta or pyroboric acids and further reaction of these with p-hydroxydiphenylamine.

Boric acid may be considered as equivalent to boric oxide plus water of crystallization-and boric oxide has been found to yield the same product as boric acid when reacted as above with p-hydroxydiphenylamine.

Hence the products of reaction of the aryl amino phenols with boric acid may be a mixture of esters of the various ortho, meta and pyro-' the symbols being as already defined.

As applied'to esters of ortho boric acid and P- Y y dip enylamine, the structures are represented as follows:

(@NGQP A large number of other hydroxy substituted aromatic secondary amines may be reacted with boric acid to give products for retarding the dete'rioration of rubber and the like, among them -being the following:

. p-p" Dilrydroxy diphenylamlne S-amino 4-hydroxy diphenylamine 3-methyl 4-hydroxy diphenylamine 2,4-diamino 4' hydroxy diphenylamine 3-methyl 4-hydroxy 4' hydroxy diphenylamine 3-chlor'4-hydroxy diphenylamine N-chlor phenyl p-aminophenol 3-nitro 4-hydroxy diphenylamine 3' methyl 4-hydroxy diphenylamine 3' methyl 2,4-hydroxy diphenylamine p-Hydroxy p ethyl diphenylamine 2-4 dihydroxy diphenylamine 2-4 dihydroxy G-methyl 4' hydroxy diphenylamine f 4-45-dihydroxy 2-2 tetra methyl diamino diphenylamin e 4-4'-dihydroxy 3-5 dimethyl diphenylamine 4 hydroxy 3-5 dimethyl diphenylamine 4-hydroxy 4' dimethylamino diphenylamine 4-hydroxy 4' amino diphenylamine 4-hydroxy phenyl beta naphthylamine lid thylamine I V 4-hydroxy 2-methyl plienyl beta naphthyle 5 Phenyl p-.hydr,oxy benzylamine Hydroxy naphthyl anthracyl amine 1-8-dihydroxy dibeta naphthyiamine 'p-Hydroxy p" ethyl diphenylam'ine p-Hydroxy p di-iso propyl diphenylamine p-Hydroxy p methyl diriaphthylamine Phenyl naphthyiol amine (alpha and beta) 2 (tolyl amino) l-hydroxy naphthalene 7,-(xylyl amino) 2-hydroxynaphthalene Phenylol naphthylamine (alpha and beta) Xylyl amino ethyl 'nap hthol p-Hydroxy p' methoxy diphenylamine. Phenyloi 'naphthylol nitrosamine (alpha and beta) 3-methoxy' 4-hydroxy amine 3-.ethoxy 4-hydroxy diphenylamine 4-4 dihydroxy 2-2 diethoxy diphenylamine 4-4 dihydroxy 2-2. dimethoxy diphenylamine p-Hydroxy phenyl p'-methoxy benzylamine p-Hydroxy phenyl 2-7 diethoxy alpha naphth'ylamine r p-Isopropenyl p' hydroxy diphenyiamine 42. p-Allyl oxy pf hydroxy diphenylamine '43. p-Phenoxy p' hydroxy diphenylamine 44. p-Hydroxy phenyl xenylamine 45. p-I-Iydroxy N-phenyl morpholine 46. 'p-Hydroxy-unsym. diphenyl hydrazine 47. p-Aminophenol The boric' acid may be reacted in various pro- 35. 4" hydroxy diplienylportions with the-hydroxy compound, including where the hydroxy compound or the. boric acid p-Hydroxy phenyl 18 dimethyl ,beta'naphmay be in molecular eitcess. Buitabie reacting proportions are from 1 to 3 mols oi the hydroxy compound'and from 1 to 2. mole of boric acid.

The materials have special and outstanding properties in connection with the preservation of rubber and vulcanized rubber goods.

The eflfectiveness or chemicals of this class for retarding deterioration of rubber is illustrated below by the results of standard accelerated ageing and flexing tests on a commercial 'tire tread compound. The parts are by weight. The control stock to which various reaction products are added, comprises Reaction product of l moi. p-bydroxydiidphenyiamine and l moi. boric ae Reaction product of 2 Innis. p-hydroxydiiihenyiamine and l moi. boric ac Reaction product of 3 mois. p-hydrnxydigihenyiamine and l moi. boric ac Press cures were made with pounds steam pressure (274 F'.) for 45, 60, '75 and 90 minutes. The average percent remaining tensile was determined after ageing, as follows:

A B C D Unaged .1 100 100 100 100 Aged 96 hours, 300 lbs.- oxygen, at

70 C 19. 7 43 40. 3 54 Aged 72 .hours in air atmospheric pressure at 100 C 46- .46. 5 51. 3 50 The increasein resistance to flex-cracking in a standard flexing test for head compounds .before and after accelerated ageing is expressed as percentage of the unaged blank .stock A.

A B c p c Unaged 100 220 218 227 Aged 48 hours in oxygen bomb 77 81 84 Aged 24 hours in air at 2l2 42 72 B0 74 The introduction of a boric acid radical into a hydroxy radical of an aryl nucleus which has no neighboring hydroxy group involves displacement of the hydrogen of the hydroxy group with formation of water during the reaction and the products may therefore be termed esters of the boric acidaand the hydroxyl compound.

The invention may be applied for the preservation of natural rubber compositions as well as artificially-prepared rubber compositions including reclaimed rubbers, and latices of such rubber compositions.

It is also to be understood that other desired filling and compounding ingredients may be incorporated along with thepreservative, for exampie, in the case of rubber, there may be incorpoi-ated other accelerators, softeners, etc.

The antioxidant may b incorporated in any type of rubber composition, such as those used in the cold by the so-called acid process.

for automobile tires and tubes, hose, belting,

sheet and thread rubber, rubberized fabrics,

molded goods, boots and shoes, etc.,'whether vulcanized in a mold, in open steam, in hot air, or The proportion of'the antioxidant may vary from about 0.1% to 5%, although either smaller or greater proportions may be found useful. If the material to which it is added is a liquid such as rubber cement or an oil, the antioxidant may be dissolved therein in a suitable small proportion. The antioxidant may be incorporated into solid substances by milling or mastication, and prepared for incorporation into dispersions or solutions'either in powder, paste or solution form,

or applied in such forms for incorporation by difl'usion, to the surfaces of vulcanized or unvulcanized rubber goods.

Having thus described -my invention, what I claim and desire to protect by Letters Patent is: l. A rubber composition containing prior to vulcanization a compound which is an ester reaction' product of a-boric acid and a monohydroxy ring substituted aromatic secondary amine.

2. A method of preserving'an organic substance which tends to deteriorate by. absorption of oxygen from the air which comprises incorporating thereina compound having the type formula where R is an arylene nucleus free from hydroxyl groups in the positions ortho to the-oxygen; n is 1; A represents an aryl group; N is nitrogen, and)! is +B(OH)2.

3. A method of preserving an organic substance which tends to deteriorate by absorption of oxygen from the air which comprises incorporating therein a compound having the type formula where R. is an arylene nucleus free from hydroxyl groups in the positions ortho to the oxygen; 12 is 2; A represents an aryl group; N is nitrogen: and X is =BOH.

4. A method of preserving an organic substance which tends to deteriorate by absorption of oxygen from the air which comprises incorporating therein a compound having the type formula H A.N.RO

where R is an arylene nucleus free from bydroxyl groups in the positions ortho to the oxygen; 11. is 3; A represents an aryl group; N is nitrogen; and X is -B.v

5. A-method of preserving rubber which comporating therein a tiiarylamine having an aryl group directly bonded to oxygen which is singly bonded to boron of a boron-containing radical derived fromboric acid, said aryl group having its nucleus free of substitutent hydroxyl groups in the positions ortho to the oxygen.-

'7. A method oi. preserving rubber which comprises incorporating therein a diarylamine having an aryl group directly bonded to oxygen which is singly bonded to boron of a boron-containing. radical derived from boric acid, said aryl group 'having its nucleus free or substituent hydroxyl groups in the positions orthol to the oxy en.

i'HILIP '1'. PAUL. 

